1. Preheat the oven to 400°F.

2. Trim and halve the Brussels sprouts while you bring a large pan of salted water to the boil.

3. Boil the sprouts for 4-5 minutes until they turn bright green, and cook until slightly tender.

4. Drain them in a colander and allow them to steam off completely, then pour them into a suitable-sized baking dish. Spread them out evenly and scatter in the red grapes.

5. In the meantime, melt the butter in a small pan and add the arrowroot powder, creating a roux.

6. Add the milk and whisk continuously until you notice the mixture thickens.

7. Season the mixture with salt and white pepper, then pour the mixture into the baking dish.

8. Scatter over the two grated cheeses.

9. Bake in the oven for 20 minutes before serving. Season with additional salt if needed.